parallelcommand in scripted pipeline.
I don't think we're willing to install a any trial plugins on that wiki instance. However, I like the idea of showing progress somewhere. We could create a ticket in Jira that tracks the progress on pages or we could extract the count of pages and compare the count of wiki pages to the count of redirects (see Gavin's proposal in the jenkinsci/docs channel)
The wiki is intentionally read only because of the spam problems that we are not willing to spend admin time to fight.